bash script for replace text from two file in one

I have two file xml; en.xml and it.xml

in the default file language en.xml I have this structure

<string key="City is not set">
    <tr lang="en"> City is not set </tr>

in the file It.xml I have:

<string key="Citt&agrave; non &egrave; impostato">
    <tr lang="it">  </tr>

In that way I can extract data from it.xml and put in to en.xml ?

from en.xml I need to get string key

<string key="City is not set">

in the second file it.xml I need to change:

<string key="Citt&agrave; non &egrave; impostato">

in to :

<tr lang="it"> Citt&agrave; non &egrave; impostato </tr>

my goal is to obtain a final result:

<string key="City is not set">
    <tr lang="it"> Citt&agrave; non &egrave; impostato </tr>

I hope is clear.